1.1 The Field of Corneal Topography and Eye Surgery
A. Corneal Measurement and Correction
The corneal surface is responsible for the majority of the refractive power of the human eye. Therefore, measurement of the cornea's surface refractive power is very important in the diagnosis and treatment of many visual disorders. A common gauge of surface refractive power is the topography of the eye's cornea. Methods of ascertaining the eye's corneal topography are comprised of interferometric, rasterstereographic and videokeratographic technologies.
Corneal topography provides information about corneal curvature that allows ophthalmic surgeons to improve surgical results. A wide variety of surgical procedures currently benefit from pre and post surgical planning with corneal topography: astigmatic keratotomy (AK); epikeratophakia (EPI); radial keratotomy (RK); Excimer laser surgery; photorefractive keratectomy (PRK); penetrating keratoplasty (PK); Thermokeratoplasty (TKP) and cataract surgery.
1.2 The Problem of Quantifying Eye Surgery
A. Information in a Corneal Topography Map
Typically, the information provided by a corneal topography map is a set of curvature points that represent the corneal surface. Each point can indicate a specific radius of curvature or dioptric power at the correlative point on the examined eye. See e.g. Koch D. D., Foulks G. N., Moran C. T., Wakil J. S., "The Corneal EyeSys System: Accuracy Analysis and Reproducibility of First-Generation Prototype,"Refract Corneal Surge., volume 5, pg 424-429, 1989.
The use of corneal topography for preoperative examination has greatly increased the accuracy, precision and amount of information in preoperative examination data. This data volume continues growing, following new developments in corneal modelling and corneal topographic measurements. See Koch D. D. supra; Belin M. W., Litoff D., Strods S. J., Winn S. S., Smith R. S., "The PAR Technology Corneal Topography System," Refract Corneal Surg., 8: 88-96, 1992. Managing this volume of data is one of the barriers to the beneficial evolution of corneal shaping techniques. This barrier is most apparent with respect to certain techniques such as astigmatic arcuate cuts. See Lundergan M. K., Rowsey J. J., "Relaxing Incisions,"Corneal Topography." Ophthalmology, 92: 1226-1236 (1985).
B. Incisions and The Use of Corneal Topography
The use of corneal topography is becoming more and more prevalent in the field of incisional refractive surgery. Incisional refractive surgery (RK & AK) involves cutting the cornea to relax and flatten selected areas in order to achieve the desired vision correction without the need of corrective lenses (specifically, glasses or contact lenses). A refractive surgeon uses a corneal topography map to plan the location of cuts to be made in the eye during surgery. This planning process involves a study of the corneal topography map to determine areas of the cornea requiring topographic change. Given this information, the surgeon can estimate the size and position of one or more cuts that will correct the problem. This procedure is entirely subjective. While viewing a corneal topography map, a surgeon estimates the size and placement of a corrective incision relying on intuition and experience. While some surgeons may use some quantitative techniques, this process yields varying results because the size and location of the incisions cannot be precisely correlated to an invariant source. This is because the method of surgery represents an acquired intuition or art on behalf of the surgeon and not an exact scientific and quantitative approach or method. Therefore, the success of a particular surgery depends largely upon the skill and experience of the specific surgeon. Furthermore, even a specific surgeon's results may vary substantially from hour to hour or day to day.